1. Field of the Invention
The present invention is directed to a method of manufacturing thin metal alloy foils using evaporative techniques. More specifically, the present invention is directed to manufacturing metal alloy foils by depositing layers of different metals and heating the layers to form the alloy.
2. Discussion of Related Art
It is desirable to manufacture thin metal alloy foils for a wide variety of applications. One such application includes separators for chemical components. This invention will be described as a method of manufacturing a thin metal foil that may be used as a separator. The separator is exposed to a mixed gas stream on one surface. The separator material allows one component of the gas stream to pass through the material and separate one selected gas at very high concentration from the mixed gas stream.
Metal separators have been used to separate hydrogen from a gas stream containing hydrogen and other gases. Hydrogen separators generally operate by catalyzing the hydrogen gas into hydrogen atoms that selectively pass through the foil. The hydrogen atoms recombine on the opposite surface of the foil to form hydrogen gas. The permeability of the separator increases as the foil thickness decreases. Thin metal foils are much more efficient in separating hydrogen gas than thicker foils.
Traditionally, the metal foils have been made by a rolling or pressing technique. An ingot of metal having a desired composition is cast and rolled or pressed into a foil. This rolling or pressing technique is only capable of producing a consistently pinhole free foil having a thickness not less than 25 microns. The foil may tear and have pinholes when it is rolled to a thickness less than 25 microns.
It is also desirable to manufacture the foil from a number of metals to form an alloy. The metal alloy has superior physical properties such as non-embrittlement, and may be more effective at separating one component from a mixed gas stream. The metal alloy has traditionally been formed by blending metal powders or shots and then heating the mixture to melt the metals. The molten metals blend and form an alloy when cooled. The alloy ingot is then rolled or pressed to form the thin metal foil.
The problem with rolling the alloy is that it takes many successive "rolls and anneals" to produce a thin film. An ingot of an alloy cannot be rolled down to the desired thickness in one trial. The ingot is rolled down a few millimeters at a time with an anneal in between each rolling action.
It is also possible to electrochemically deposit metal onto a surface such as a ceramic or metal substrate. Very thin coatings are possible using this technique. Electroless plating is an example of an electrochemically deposited metal. The problem with electroless plating is that it introduces unwanted elements to the material. The present invention is intended to produce self supporting foils that will be used independently from the carrier and have a high degree of elemental purity.
The present invention attempts to provide a method of manufacturing thin alloy foils that does not utilize a rolling or pressing process. The method enables the manufacture of very thin foils having metallurgical compositions not attainable through conventional alloying methods. These and other disadvantages of the related arts are overcome by the method described herein.